Power level settings for transmission lines

ABSTRACT

A method, wherein the following steps are iteratively repeated: providing each of a plurality of signals at a respective one of a plurality of transmission links; transmitting each of the plurality of signals over the respective one of the plurality of transmission links; and measuring signal-to-noise ratios of the plurality of signals transmitted over the plurality of transmission links, wherein an input power level of each of the plurality of signals is set such that the signal-to-noise ratios of the plurality of signals converge when measured after their transmission over the plurality of transmission links.

TECHNICAL FIELD

This invention relates to transmission lines in general and moreparticularly to power level settings for bundled transmission lines.

BACKGROUND

Telecommunication and broadband services are usually provided tocustomer premises via twisted pairs of wires. The twisted pairs areoften grouped in close proximity into binder groups. Data transmissionin these settings may suffer from interference arising fromelectromagnetic coupling between neighboring twisted pairs, referred toas crosstalk interference.

SUMMARY

A method may comprise the following steps that are iteratively repeated:providing each of a plurality of signals at a respective one of aplurality of transmission links; transmitting each of the plurality ofsignals over the respective one of the plurality of transmission links;and measuring signal-to-noise ratios of the plurality of signalstransmitted over the plurality of transmission links, wherein an inputpower level of each of the plurality of signals is set such that thesignal-to-noise ratios of the plurality of signals converge whenmeasured after their transmission over the plurality of transmissionlinks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a network of a plurality oftransmission lines L₁ to L_(M) according to an embodiment.

FIG. 2 illustrates a model of a transmission system.

FIG. 3 illustrates an interference channel model showing crosstalkinterference among the transmission lines L₁ to L_(M).

FIG. 4 illustrates the convergence of an iterative method according toan embodiment.

FIGS. 5A to 5C illustrate exemplary results of a simulation of aniterative method according to an embodiment.

FIGS. 6A to 6C illustrate exemplary results of a simulation of aniterative method according to an embodiment.

FIG. 7 illustrates exemplary results of a simulation of an iterativemethod according to an embodiment.

FIG. 8 illustrates definitions of variables a and b.

FIG. 9 illustrates exemplary results of a simulation of an iterativemethod according to an embodiment.

FIG. 10 illustrates frequency band allocation of an exemplary VDSLnetwork.

FIG. 11 illustrates an assumed power spectral density of alien noise.

FIG. 12 illustrates line attenuations of the shortest and the longesttransmission line.

FIG. 13 illustrates minimum and maximum FEXT attenuations.

FIG. 14 illustrates exemplary results of a simulation of an iterativemethod according to an embodiment.

FIG. 15 illustrates exemplary results of a simulation of an iterativemethod according to an embodiment.

FIG. 16 illustrates spectral power densities for the shortest and thelongest transmission line.

FIG. 17 illustrates exemplary results of a simulation of an iterativemethod according to an embodiment.

DETAILED DESCRIPTION

In the following one or more embodiments are described with reference tothe drawings, wherein like reference numerals are generally utilized torefer to like elements throughout, and wherein the various structuresare not necessarily drawn to scale. In the following description, forpurposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of one or more aspects ofembodiments. It may be evident, however, to one skilled in the art thatone or more aspects of the embodiments may be practiced with a lesserdegree of these specific details. In other instances, known structuresand devices are shown in block diagram form in order to facilitatedescribing one or more aspects of the embodiments. The followingdescription is therefore not to be taken in a limiting sense, and thescope of the invention is defined by the appended claims.

Referring to FIG. 1, a schematic diagram of a network of a plurality oftransmission lines L₁ to L_(M) is shown. The transmission lines L₁ toL_(M) are bundled together within a cable C over a length l₀. Thenetwork has a central office CO comprising a plurality of transceiversLT₁ to LT_(M) coupled to the respective ends of the transmission linesL₁ to L_(M). At the subscriber premises transceivers RT₁ to RT_(M) arecoupled to the other respective ends of the transmission lines L₁ toL_(M). The transceivers RT₁ to RT_(M) may, for example, be modems. Datatransmission from the central office CO to a subscriber is calleddownstream data transmission, whereas data transmission from asubscriber to the central office CO is called upstream datatransmission.

According to one embodiment, at least two of the transmission lines L₁to L_(M) have different lengths. In the network shown in FIG. 1 thelength of a transmission line L_(i) is the sum of the length l₀ and alength l_(i) (i=1, . . . , M). The length l₀ is the length over whichthe transmission lines L₁ to L_(M) are bundled together and occupy thesame cable C. The length l_(i) is the length from the end of the cable Cto the transceiver RT_(i). Each of the transmission lines L₁ to L_(M)may, for example, be a pair of twisted wires.

According to a further embodiment, the cable C further comprisestransmission lines L_(ext), which are not coupled to the central officeCO.

According to yet a further embodiment, each of the transmission lines L₁to L_(M) forms a telecommunication channel. Since voice telephony usesonly a small fraction of the bandwidth usually available on thetransmission lines L₁ to L_(M), the remaining fraction of the availablebandwidth may be used for transmitting data. For data transmission thereare a number of services available, such as ISDN (Integrated ServicesDigital Network) or ADSL (Asymmetric Digital Subscriber Line) or VDSL(Very high bit-rate Digital Subscriber Line) or VDSL2 (Very highbit-rate Digital Subscriber Line 2).

Due to the close proximity of the transmission lines L₁ to L_(M) withinthe cable C of the length l₀, there is considerable amount of crosstalkinterference between different neighboring transmission lines L₁ toL_(M). Physically, there are two types of interference: near-endcrosstalk (NEXT) and far-end crosstalk (FEXT).

NEXT refers to interference between neighboring transmission lines L₁ toL_(M) that arises when signals are transmitted in opposite directions.If the neighboring lines carry the same type of service, then theinterference is called self-NEXT.

FEXT refers to interference between neighboring transmission lines L₁ toL_(M) that arises when signals are transmitted in the same direction. Ifthe neighboring transmission lines L₁ to L_(M) carry the same type ofservice, then the interference is called self-FEXT.

Furthermore, noise can be coupled to the transmission lines L₁ to L_(M)that is generated by other sources than neighboring transmission linesL₁ to L_(M). This noise is called alien noise and may, for example, begenerated by the transmission lines L_(ext).

In case of NEXT and FEXT, the interfering signals coupled to thetransmission lines L₁ to L_(M) depend on the power levels of the signalstransmitted over the transmission lines L₁ to L_(M). If signals havingthe same power level are inputted simultaneously in each of thetransmission lines L₁ to L_(M), the signal-to-noise ratio of atransmission line having a longer length will be worse than thesignal-to-noise ratio of a shorter transmission line. The reason is thatthe longer the length of the transmission line, the more the signaltransmitted over the transmission line is attenuated.

According to one embodiment, input power levels p(k_(max))₁ top(k_(max))_(M) for the transmission lines L₁ to L_(M) are determined,which allow the same transmission behavior for all subscribers coupledto the transmission lines L₁ to L_(M). For these purposes, an iterativemethod is employed with k being the iteration index (k=1, . . . ,k_(max)). At each iteration cycle k, signals u (k)₁ to u(k)_(M) areprovided to the transmission lines L₁ to L_(M) having input power levelsp(k)₁ to p(k)_(M). The signals u(k)₁ to u(k)_(M) are transmitted overthe transmission lines L₁ to L_(M) and signals y(k)₁ to y(k)_(M) arereceived at the other ends of the transmission lines L₁ to L_(M). Whenreceiving the transmitted signals y(k)₁ to y(k)_(M) signal-to-noiseratios Sn(k)₁ to Sn(k)_(M) of the transmitted signals y(k)₁ to y(k)_(M)are measured. The aforementioned steps are iteratively repeated, whereinthe input power levels p(k)₁ to p(k)_(M) of the signals u(k)₁ tou(k)_(M) when provided to the transmission lines L₁ to L_(M) are set insuch a manner that the signal-to-noise ratios Sn(k)₁ to Sn(k)_(M)converge.

According to a further embodiment, the transmission lines L₁ to L_(M)may be wireless transmission links. When it is referred to transmissionlines in the following, the transmission lines may therefore also bereplaced by wireless transmission links.

According to a further embodiment, xDSL is used as service fortransmitting data over the transmission lines L₁ to L_(M).

According to a further embodiment, signals u(k)₁ to u(k)_(M) aretransmitted in upstream direction over the transmission lines L₁ toL_(M).

According to a further embodiment, the iterative method is performedduring the initialization of the central office CO.

According to a further embodiment, the input power levels p(k_(max))₁ top(k_(max))_(M) are used for transmitting further signals u₁ to u_(M)over the transmission lines L₁ to L_(M).

According to a further embodiment, the signals u(k)₁ to u(k)_(M) arestatistically selected data modulated on a transmission frequency.

According to a further embodiment, the input power levels p(k+1)₁ top(k+1)_(M) of the signals u(k+1)₁ to u(k+1)_(M) when provided to thetransmission lines L₁ to L_(M) during an iteration cycle k+1 depend onthe measured signal-to-noise ratios Sn(k)₁ to Sn(k)_(M) measured duringthe previous iteration cycle k.

According to a further embodiment, the input power level p(k+1)_(i) ofthe signal u(k+1)_(i) (i=1, . . . , M) when provided to the transmissionline L_(i) during an iteration cycle k+1 is a function F of thedifference of the measured signal-to-noise ratio Sn(k)_(i) of the signaly(k)_(i) transmitted over the transmission line L_(i) during theprevious iteration cycle k and an average value avg of thesignal-to-noise ratios Sn(k)₁ to Sn(k)_(M) measured during the previousiteration cycle k:p(k+1)_(i) =F[Sn(k)_(i)−avg(Sn(k)₁, . . . , Sn(k)_(M))].  (1)

According to a further embodiment, the input power level p(k+1)_(i) ofthe signal u(k+1)_(i) (i=1, . . . , M) when provided to the transmissionline L_(i) during an iteration cycle k+1 depends on a product having atleast a factor F₁ and a factor F₂. The factor F₁ is a function of theinput power level p(k)_(i) of the signal u(k)_(i) when provided to thetransmission line L_(i) during the previous iteration cycle k. Thefactor F₂ is a function of the difference of the measuredsignal-to-noise ratio Sn(k)_(i) of the signal y(k)_(i) transmitted overthe transmission line L_(i) during the previous iteration cycle k and anaverage value avg of the signal-to-noise ratios Sn(k)₁ to Sn(k)_(M)measured during the previous iteration cycle k:p(k+1)_(i) =F ₁ [p(k)_(i) ]·F ₂ [Sn(k)_(i)−avg(Sn(k)₁ , . . . ,Sn(k)_(M))].  (2)

According to a further embodiment, the input power levels p(1)₁ top(1)_(M) of the signals u(1)₁ to u(1)_(M) at the first iteration cycle(k=1) are predetermined. For example, the input power levels p(1)₁ top(1)_(M) are set to the highest power level.

According to a further embodiment, the input power level p(2)_(i) of thesignal u(2)_(i) (i=1, . . . , M) at the second iteration cycle (k=2)depends on the inverted value of the measured signal-to-noise ratioSn(1)_(i) of the transmitted signal y(1)_(i) of the first iterationcycle (k=1).

According to another embodiment, a method refers to a plurality oftransmission lines L₁ to L_(M) each having an input terminal and anoutput terminal. Referring to FIG. 1, the input terminals may, forexample, be the transceivers LT₁ to LT_(M) of the central office CO andthe output terminals may be the transceivers RT₁ to RT_(M) at thesubscribers end or vice versa.

According to the method of the present embodiment, first signals u(k)₁to u(k)_(M) are provided to the input terminals and transmitted over thetransmission lines L₁ to L_(M). At the output terminals of thetransmission lines L₁ to L_(M) transmitted first signals y(k)₁ toy(k)_(M) are received. Further, signal-to-noise ratios Sn(k)₁ toSn(k)_(M) of the transmitted first signals y(k)₁ to y(k)_(M) aremeasured at the output terminals of the transmission lines L₁ to L_(M).Subsequently, second signals u(k+1)₁ to u(k+1)_(M) are provided to theinput terminals and are transmitted over the transmission lines L₁ toL_(M). The input power levels p(k+1)₁ to p(k+1)_(M) of the secondsignals u(k+1)₁ to u(k+1)_(M) are set depending on the measuredsignal-to-noise ratios Sn(k)₁ to Sn(k)_(M) of the afore transmittedfirst signals y(k)₁ to y(k)_(M).

The measured signal-to-noise ratios Sn(k)₁ to Sn(k)_(M) of thetransmitted first signals y(k)₁ to y(k)_(M) are distributed over a firstrange of signal-to-noise ratios. The distribution of the measuredsignal-to-noise ratios Sn(k)₁ to Sn(k)_(M) thus defines the first range.According to one embodiment, the input power levels p(k+1)₁ top(k+1)_(M) of the second signals u(k+1)₁ to u(k+1)_(M) are set in such amanner that the signal-to-noise ratios Sn(k+1)₁ to Sn(k+1)_(M) of thesecond signals y(k+1)₁ to y(k+1)_(M) after their transmission over thetransmission lines L₁ to L_(M) are distributed over a second range ofsignal-to-noise ratios which is smaller than the first range. Thisprocedure results in a convergence of the signal-to-noise ratios.

According to another embodiment, a transfer function of each of thetransmission lines L₁ to L_(M) is determined and information related tointerference characteristics of each of the transmission lines L₁ toL_(M) is collected. Furthermore, the transfer functions and theinformation related to interference characteristics are used todetermine input power levels p₁ to p_(M) of signals u₁ to u_(M) in sucha manner that, when providing the signals u₁ to u_(M) to the inputterminals of the transmission lines L₁ to L_(M) and measuring thesignal-to-noise ratios Sn₁ to Sn_(M) of the transmitted signals y₁ toy_(M) at the output terminals of the transmission lines L₁ to L_(M), thesignal-to-noise ratios Sn₁ to Sn_(M) are essentially equal. For example,the signal-to-noise ratios Sn₁ to Sn_(M) are essentially equal if thesignal-to-noise ratios Sn₁ to Sn_(M) are within a predetermined range ora predetermined error range.

According to another embodiment, input power levels {tilde over (p)}(0)₁to {tilde over (p)}(0)_(M) for the transmission lines L₁ to L_(M) areprovided. The input power levels {tilde over (p)}(0)₁ to {tilde over(p)}(0)_(M) are provided in such a manner that when signals ũ(0)₁ toũ(0)_(M) having the input power levels {tilde over (p)}(0)₁ to {tildeover (p)}(0)_(M) are provided to the transmission lines L₁ to L_(M),signals {tilde over (y)}(0)₁ to {tilde over (y)}(0)_(M) are received atthe other ends of the transmission lines L₁ to L_(M) having essentiallyequal signal-to-noise ratios {tilde over (S)}n(0)₁ to {tilde over(S)}n(0)_(M). For example, the input power levels {tilde over (p)}(0)₁to {tilde over (p)}(0)_(M) resulting in equal signal-to-noise ratios{tilde over (S)}n(0)₁ to {tilde over (S)}n(0)_(M) may be determined byusing one of the methods described above. The signal-to-noise ratios{tilde over (S)}n(0)₁ to {tilde over (S)}n(0)_(M) are essentially equalif the signal-to-noise ratios {tilde over (S)}n(0)₁ to {tilde over(S)}n(0)_(M) are within a predetermined range or a predetermined errorrange.

Subsequently, the following steps are iteratively repeated. Signalsũ(k)₁ to ũ(k)_(M) are provided to the transmission lines L₁ to L_(M)(k=1, 2, . . . ). The signals ũ(k)₁ to ũ(k)_(M) are transmitted over thetransmission lines L₁ to L_(M) and signals {tilde over (y)}(k)₁ to{tilde over (y)}(k)_(M) are received at the other ends of thetransmission lines L₁ to L_(M). The signal-to-noise ratios {tilde over(S)}n(k)₁ to {tilde over (S)}n(k)_(M) of the transmitted signals {tildeover (y)}(k)₁ to {tilde over (y)}(k)_(M) are measured. At each iterationcycle k+1 the input power level {tilde over (p)}(k+1)_(i) of the signalũ(k+1)_(i) (i=1, . . . , M−1) is greater than the input power level{tilde over (p)}(k)_(i) of the signal ũ(k)_(i) of the previous iterationcycle k.

According to a further embodiment, the method is terminated or at leastinterrupted when at least one of the measured signal-to-noise ratios{tilde over (S)}n(k)₁ to {tilde over (S)}n(k)_(M) exceeds apredetermined threshold.

According to a further embodiment, the input power level {tilde over(p)}(k+1)_(i) of the signal ũ(k+1)_(i) (i=1, . . . , M−1) when providedto the transmission line L_(i) during an iteration cycle k+1 depends ona product having at least a factor F₁ and a factor F₂. The factor F₁ isa function of the input power level {tilde over (p)}(k)_(i) of thesignal ũ(k)_(i) provided to the transmission line L_(i) during theprevious iteration cycle k. The factor F₂ depends on a linear functionor an exponential function or a logarithmic function of the input powerlevel {tilde over (p)}(k)_(i) of the signal ũ(k)_(i) of the previousiteration cycle k:{tilde over (p)}(k+1)_(i) =F ₁ [{tilde over (p)}(k)_(i) ]·F ₂ [{tildeover (p)}(k)_(i)].  (3)

In the following another embodiment is described in more detail. In thisembodiment the frequency band used for transmitting signals indownstream direction is different from the frequency band used fortransmitting signals in upstream direction. As a consequence, self-NEXTcan be excluded as a source of interference, however self-FEXT must beconsidered. For example, VDSL or ADSL may be used as services fortransmitting data over the transmission lines and DMT (DiscreteMulti-Tone) modulation may be used for modulating signals, however theembodiment described in the following is not limited thereto. Thepresent embodiment may be also applied to a system which uses the samefrequency band, but different time slots for downstream and upstreamdirections.

The network of the transmission lines L₁ to L_(M) of the presentembodiment is shown in FIG. 1. The transceivers LT₁ to LT_(M) of thecentral office CO as well as the transceivers RT₁ to RT_(M) at thesubscriber premises comprise units which allow to measure thesignal-to-noise ratios of signals received over the respectivetransmission lines L₁ to L_(M). The values of the measuredsignal-to-noise ratios are transferred to a central control unit CCU,which is coupled to the central office CO. The central control unit CCUsets the power levels of the signals transmitted by the transceivers LT₁to LT_(M) and RT₁ to RT_(M). Special transmission and control channelsare provided between the central office CO and the transceivers RT₁ toRT_(M) in order to exchange data between the central control unit CCUand the transceivers RT₁ to RT_(M).

FIG. 2 illustrates a model of the transmission system of the presentembodiment. The model only considers the transmission lines L₁ to L_(M)which are coupled to the central office CO. The arrows between thetransceivers LT_(i) and RT_(i) illustrate the logical connectionsbetween the transceivers LT_(i) and RT_(i) (i=1, . . . , M). Since it isassumed that there is no crosstalk interference between downstream andupstream directions, the power levels in downstream and upstreamdirections can be determined separately.

As can be seen from FIG. 2, self-FEXT signals fext and interferingsignals r disturb the signals transmitted between the transceiversLT_(i) and RT_(i). The interfering signals r are caused by alien noisewhich may be due to the transmission lines L_(ext), which are notcoupled to the central office CO, and other external sources.

In FIG. 3 an interference channel model is illustrated exhibitingcrosstalk interference among the transmission lines L₁ to L_(M) ineither downstream or upstream direction. A signal u_(i) is provided tothe input terminal of a transmission line L_(i) and a signal y_(i) isreceived at the output terminal of the transmission line L_(i) (i=1, . .. , M). A transfer function H_(ij) is the transfer function of a channelfrom the input terminal of a transmission line L_(i) to the outputterminal of the transmission line L_(j) for a specific frequency channel(j=1, . . . , M). The transfer functions H_(ii) are the transferfunctions of the transmission lines L₁ to L_(M) and the transferfunctions H_(ij,i≠j) are the crosstalk transfer functions.

According to the interference channel model shown in FIG. 3, the signaly_(i) received at the output terminal of the transmission line L_(i) isas follows:

$\begin{matrix}{y_{i} = {{u_{i} \cdot H_{ii}} + {\sum\limits_{{j = 1},{j \neq i}}^{M}{u_{j\;} \cdot H_{ij}}} + {r_{i}.}}} & (4)\end{matrix}$

Assuming that the signals transmitted over different transmission linesare not correlated, the signal-to-noise ratio Sn_(i) at the outputterminal of the transmission line L_(i), which is the ratio between thepower S of the wanted signal and the power N of the noise, is given bythe following equation:

$\begin{matrix}{{Sn}_{i} = {\left( \frac{S}{N} \right)_{i} = {\frac{\left\langle u^{2} \right\rangle_{i} \cdot {H_{ii}}^{2}}{{\sum\limits_{{j = 1},{j \neq 1}}^{M}{\left\langle u^{2} \right\rangle_{j} \cdot {H_{ij}}^{2}}} + \left\langle r^{2} \right\rangle_{i}}.}}} & (5)\end{matrix}$

Since many signals have a very wide dynamic range, signal-to-noiseratios are usually expressed in terms of the logarithmic decibel scale.In decibels, the logarithmic signal-to-noise ratio Sndb_(i) is 10 timesthe logarithm of the power ratio Sn_(i):

$\begin{matrix}{{Sndb}_{i} = {10 \cdot {\log_{10}\left( \left( \frac{S}{N} \right)_{i} \right)}}} & (6)\end{matrix}$

In order to be able to transmit high bit rates, the values of thesignal-to-noise ratio Sn_(i) should be large. The number e of bits,which can be transmitted per frequency channel and data symbol, is:

$\begin{matrix}{e = {{floor}\left( {\log_{2}\left( {1 + \frac{Sn}{{Sn}_{ref}}} \right)} \right)}} & (7)\end{matrix}$Sn_(ref) is a reference signal-to-noise ratio, which depends on thewanted bit error rate, the margins and the coding gain.

As can be seen from equation (5), the signal-to-noise ratio Sn_(i)measured at the output terminal of the transmission line L_(i) dependson the power levels of the signals u₁ to u_(M), the transfer functionH_(ii), the transfer functions H_(ij,j≠1) and the power level of thealien noise interference signal r_(i). Two extreme cases may arise:

-   (a) FEXT can be neglected compared to alien noise. In this case the    signal-to-noise ratio Sn_(i) only depends on the input power level    of the signal u_(i). In order to achieve a high signal-to-noise    ratio Sn_(i), it is favorable to feed the transmission lines L₁ to    L_(M) with signals u₁ to u_(M) at the highest power level.-   (b) Alien noise can be neglected compared to FEXT. In this case the    signal-to-noise ratio Sn_(i) depends on the input power levels of    all signals u₁ to U_(M). If the signals u₁ to u_(M) have equal input    power levels, shorter transmission lines L_(i) produce better    signal-to-noise ratios Sn_(i).

A conditional equation for the transfer function H_(ij) can be derived:|H _(ij)(f)|=K _(ij) ·f·√{square root over (l ₀)}·|H _(line)(f)|  (8)

Based on a more realistic model, the following equation was found forthe transfer function H_(ij):

$\begin{matrix}{{{H_{ij}(f)}} = {K_{ij} \cdot f \cdot \sqrt{1_{0}} \cdot {{H_{line}(f)}} \cdot \left\lbrack {1 + {3 \cdot {\cos\left( \frac{2 \cdot \pi \cdot 1_{0}}{c_{line}} \right)}} - {3 \cdot {\sin\left( \frac{2 \cdot \pi \cdot 1_{0}}{c_{line}} \right)}}} \right\rbrack}} & (9)\end{matrix}$

In equations (8) and (9) f is the frequency, l₀ is the length of thecable C which binds the transmission lines L_(i) and L_(j) together,K_(ij) is a frequency- and length-independent factor, which depends onphysical and geometrical features of the cable C, H_(line) (f) is thefrequency response of the transmission lines L_(i) and L_(j) and c isthe speed of light in the transmission lines L_(i) and L_(j), which isroughly 200,000 km/s.

In the following a method is discussed as an exemplary embodiment, whichallows to determine the input power levels p₁ to p_(M) for signalsprovided to the input terminals of the transmission lines L₁ to L_(M) sothat the signals received at the output terminals of the transmissionlines L₁ to L_(M) exhibit equal signal-to-noise ratios Sn₁ to Sn_(M). Asa result the same maximal data rate can be transmitted over thetransmission lines L₁ to L_(M). The method is performed either fordownstream or for upstream direction and for a single frequency channel.

The input power levels p₁ to p_(M) of the signals provided to thetransmission lines L₁ to L_(M), the signal-to-noise ratios Sn₁ to Sn_(M)measured at the output terminals of the transmission lines L₁ to L_(M)and the logarithmic signal-to-noise ratios Sndb₁ to Sndb_(M) arecombined in vectors p, Sn and Sndb, respectively:

$\begin{matrix}{p = \begin{bmatrix}p_{1} \\p_{2} \\\vdots \\p_{M}\end{bmatrix}} & (10) \\{{Sn} = \begin{bmatrix}{Sn}_{1} \\{Sn}_{2} \\\vdots \\{Sn}_{M}\end{bmatrix}} & (11) \\{{Sndb} = {\begin{bmatrix}{Sndb}_{1} \\{Sndb}_{2} \\\vdots \\{Sndb}_{M}\end{bmatrix}.}} & (12)\end{matrix}$

According to one embodiment, at the first cycle of the method, which isdenoted with k=1, signals are simultaneously provided to thetransmission lines L₁ to L_(M) having the highest input power levelp_(max):

$\begin{matrix}{{p\left( {k = 1} \right)} = \begin{bmatrix}p_{\max} \\p_{\max} \\\vdots \\p_{\max}\end{bmatrix}} & (13)\end{matrix}$

The signal-to-noise ratios Sn(1)₁ to Sn(1)_(M) of the signals, which arereceived at the output terminals of the transmission lines L₁ to L_(M),are measured. According to a further embodiment, the signal-to-noiseratios Sn(1)₁ to Sn(1)_(M) measured in the first cycle of the method(k=1) are used for determining the input power levels p(k=2) of thesecond cycle:

$\begin{matrix}{{p\left( {k = 2} \right)} = {\begin{bmatrix}\left( \frac{1}{{{Sn}(1)}_{1}} \right) \\\left( \frac{1}{{{Sn}(1)}_{2}} \right) \\\vdots \\\left( \frac{1}{{{Sn}(1)}_{M}} \right)\end{bmatrix}.}} & (14)\end{matrix}$

According to one embodiment, the vector p(2) is scaled:

$\begin{matrix}{{\hat{p}(2)} = {{p(2)} \cdot \frac{p_{\max}}{\max\left( {p(2)} \right)}}} & (15)\end{matrix}$In equation (15) max(p(2)) denotes the maximum component of the vectorp(2) of equation (14). The scaling prevents exceeding the maximum powerlevel p_(max).

The scaled vector {circumflex over (p)}(2) provides the input powerlevels for the signals provided to the input terminals of thetransmission lines L₁ to L_(M) during the second cycle of the method. Atthe output terminals of the transmission lines L₁ to L_(M) thesignal-to-noise ratios Sn(2)₁ to Sn(2)_(M) or the logarithmicsignal-to-noise ratios Sndb(2)₁ to Sndb(2)_(M) are measured.Transmitting signals over the transmission lines L₁ to L_(M) andmeasuring their signal-to-noise ratios Sn(k)₁ to Sn(k)_(M) or theirlogarithmic signal-to-noise ratios Sndb(k)₁ to Sndb(k)_(M) is theniteratively repeated.

The iterations are repeated until the measured signal-to-noise ratiosSn(k)₁ to Sn(k)_(M) or the measured logarithmic signal-to-noise ratiosSndb(k)₁ to Sndb(k)_(M) reach sufficient convergence (k=k_(max)). Ateach of the iteration cycles k=2 to k=k_(max)−1 the signal-to-noiseratios Sn(k)₁ to Sn(k)_(M) or the logarithmic signal-to-noise ratiosSndb(k)₁ to Sndb(k)_(M) of the signals received at the output terminalsof the transmission lines L₁ to L_(M) are measured and used for settingthe input power levels p(k+1) of the signals provided to the inputterminals of the transmission lines L₁ to L_(M) during the nextiteration cycle k+1:p(k+1)=p(k)·|1−g·x(k)|  (16)In equation (16) g is a predetermined constant, which influences theconvergence of the method, and x(k) is calculated as follows:

$\begin{matrix}{{x(k)} = {{{Sndb}(k)} - {\frac{1}{M}{{{\sum\limits_{i = 1}^{M}{{Sndb}(k)}_{i}}}.}}}} & (17)\end{matrix}$

Before the determined input power levels are used for providing signalsto the transmission lines L₁ to L_(M), the vector p(k+1) may be scaled:

$\begin{matrix}{{\hat{p}\left( {k + 1} \right)} = {{p\left( {k + 1} \right)} \cdot {\frac{p_{\max}}{\max\left( {p\left( {k + 1} \right)} \right)}.}}} & (18)\end{matrix}$In equation (18) max(p(k+1)) denotes the maximum component of the vectorp(k+1). The scaled vector {circumflex over (p)}(k+1) is used forproviding signals to the transmission lines L₁ to L_(M) at the iterationcycle k+1.

In the following a simulation is presented which illustrates the methoddescribed above. The simulated network comprises 50 transmission linesL₁ to L₅₀. The lengths of the transmission lines L₁ to L₅₀ are evenlydistributed between 200 m and 800 m. The network is based on a model asshown in FIG. 3. FIG. 4 illustrates the convergence of the appliediterative method. In FIG. 4 a difference d(k) is plotted versus theiteration index k. The difference d(k) is the difference between themaximum logarithmic signal-to-noise ratio and the minimum logarithmicsignal-to-noise ratio measured at each iteration cycle k:d(k)=max(Sndb(k))−min(Sndb(k))  (19)

The upper diagram of FIG. 4 shows the difference d(k) on a linear scale,whereas the lower diagram of FIG. 4 shows the difference d(k) on alogarithmic scale. It can be seen from FIG. 4 that the difference d(k)between the maximum logarithmic signal-to-noise ratio and the minimumlogarithmic signal-to-noise ratio becomes smaller than 0.01 dB after 6iteration cycles which means that the logarithmic signal-to-noise ratiosmeasured at the output terminals of the transmission lines L₁ to L₅₀have sufficiently converged at this point in time.

FIGS. 5 and 6 show plots of the input power level p versus the length lof the transmission lines and plots of the resulting logarithmicsignal-to-noise ratios Sndb versus the length l in the presence of onlyFEXT (cf. FIGS. 5A and 6A), FEXT and alien noise (cf. FIGS. 5B and 6B)as well as only alien noise (cf. FIGS. 5C and 6C). FIG. 5 refers tosignals transmitted in upstream direction and FIG. 6 refers to signalstransmitted in downstream direction. Data illustrated by dashed lineswere recorded when the maximum power level p_(max) (=0 dB) was used forproviding signals to the transmission lines L₁ to L₅₀. Data illustratedby continuous lines were recorded after the iterative method describedabove had reached convergence (k=k_(max)).

It is evident from FIGS. 5 and 6 that performing the iterative methoddescribed above results in a convergence of the signal-to-noise ratiosof all transmission lines. It can be further seen from FIGS. 5 and 6that the more FEXT interference occurs, the more the iterative methodleads to an improvement of the signal-to-noise ratios of the longtransmission lines, whereas the signal-to-noise ratios of the shorttransmission lines are decreased due to the iterative method.

Further, a comparison of the FIGS. 5 and 6 reveals that the improvementof the behavior of the longer transmission lines is more striking forthe upstream direction than for the downstream direction.

FIG. 7 illustrates the simulated behavior of a further network. Thesimulated network comprises 50 transmission lines L₁ to L₅₀, the lengthsof which are statistically distributed between 200 m and 800 m.Moreover, the factor K_(ij) and the alien noise are also statisticallydistributed to a certain degree. In FIG. 7 a plot of the input powerlevel p versus the length l of the transmission lines and a plot of theresulting logarithmic signal-to-noise ratio Sndb versus the length l inthe presence of FEXT and alien noise are shown. The data shown in FIG. 7were recorded in upstream direction. Data illustrated by dashed lineswere recorded when the maximum input power level p_(max) (=0 dB) wasused for the providing signals to the transmission lines L₁ to L₅₀. Dataillustrated by continuous lines were recorded after the iterative methodhad reached convergence.

Since the method according to the embodiment described above improvesthe signal-to-noise ratios of longer transmission lines especially ifFEXT is the dominant source of interference, it is interesting to know ameasure of the presence of FEXT compared to alien noise. Such a measureis given by a variable η:

$\begin{matrix}{\eta = \frac{a}{b}} & (20)\end{matrix}$In equation (20) variables a and b are introduced. The variables a and bare defined as follows:a=max(Sndb(1))−min(Sndb(k _(max)))  (21)b=max(Sndb(1))−min(Sndb(1))  (22)In equations (21) and (22) the terms max (Sndb(1)) and min (Sndb(1))denote the maximum and minimum components of the vector Sndb at k=1,respectively, when signals are provided to the transmission lines at themaximum power level. The term min (Sndb(k_(max))) denotes the maximumcomponent of the vector Sndb when the iterative method has reachedsufficient convergence meaning min (Sndb(k_(max)))≈max (Sndb(k_(max))).The definitions of the variables a and b are also illustrated in FIG. 8.

If FEXT does not occur, the variable η is one. The higher the presenceof FEXT, the more the variable η decreases.

In the following a further iterative method according to one embodimentis described which improves the signal-to-noise ratios of the shortertransmission lines compared to the iterative method described above. Theimprovement is achieved by successively increasing the input powerlevels of the signals provided to the transmission lines L₁ to L_(M−1)until the logarithmic signal-to-noise ratio obtained from at least onetransmission line, which is usually the longest transmission line L_(M),falls below a predetermined threshold value Sndb_(min). The input powerlevel of the signals provided to the longest transmission line L_(M) iskept constant.

Before starting the iterative method presented in the following inputpower levels {tilde over (p)}(0)_(i) (i=1, . . . , M) must be known,which, when used for providing signals to the transmission lines L₁ toL_(M), produce equal logarithmic signal-to-noise ratios at the outputterminals of the transmission lines L₁ to L_(M). For example, the inputpower levels {tilde over (p)}(0)_(i) are given by the input power levelsp(k_(max))_(i), which are obtained in the final iteration cycle k_(max)of the iterative method presented above and which produced an equallogarithmic signal-to-noise ratio Sndb(k_(max))_(i) for all transmissionlines L₁ to L_(M).

Starting from the input power levels {tilde over (p)}(0)_(i), the inputpower levels are successively increased at each iteration cycle untilthe logarithmic signal-to-noise ratio measured at the output terminal ofat least one transmission line L_(i) is reduced by more than apredetermined parameter Δdb compared to the logarithmic signal-to-noiselevel Sndb(k_(max))_(i).

According to one embodiment, before starting the iterative method it isverified whether Δdb<b−a. If this inequation is false, the maximum powerlevel p_(max) is chosen for all of the transmission lines L₁ to L_(M)and the iterative method is not performed any further. If the inequationis true, the iterative method is started.

The iteration cycles of the method are denoted with {tilde over (k)}(=1, 2, . . . ). At the beginning of each iteration cycle signals areprovided to the input terminals of the transmission lines L₁ to L_(M).The signals are received at the output terminals of the transmissionlines L₁ to L_(M) and the logarithmic signal-to-noise ratios Sndb({tildeover (k)})_(i) are measured for each signal. The input power levels{tilde over (p)}({tilde over (k)}) for each iteration cycle {tilde over(k)} are given by the following equations:

$\begin{matrix}{{\overset{\sim}{p}\left( \overset{\sim}{k} \right)} = \begin{bmatrix}{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{1} \\{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{2} \\\vdots \\{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{M}\end{bmatrix}} & (23)\end{matrix}${tilde over (p)}({tilde over (k)}+1)={tilde over (p)}({tilde over(k)})·|1−{tilde over (g)}·{tilde over (d)}({tilde over (k)})  (24){tilde over (p)}(0)=p(k _(max)).  (25)In equation (24) {tilde over (g)} is a predetermined constant, whichinfluences the convergence of the method, and {tilde over (d)}({tildeover (k)}) is a vector of functions {tilde over (F)} of the input powerlevels {tilde over (p)}({tilde over (k)})_(i), which will be discussedin more detail later:

$\begin{matrix}{{\overset{\sim}{d}\left( \overset{\sim}{k} \right)}_{i} = {\overset{\sim}{F}\left( \frac{{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{i}}{p_{\max}} \right)}} & (26)\end{matrix}$Before the input power levels {tilde over (p)}({tilde over (k)}+1)_(i)are used for providing signals to the transmission lines L₁ to L_(M),the vector {tilde over (p)}({tilde over (k)}+1) may be scaled:

$\begin{matrix}{{\hat{\overset{\sim}{p}}\left( {\overset{\sim}{k} + 1} \right)} = {{\overset{\sim}{p}\left( {\overset{\sim}{k} + 1} \right)} \cdot \frac{p_{\max}}{\max\left( {\overset{\sim}{p}\left( {\overset{\sim}{k} + 1} \right)} \right)}}} & (27)\end{matrix}$In equation (27) max({tilde over (p)}({tilde over (k)}+1)) denotes themaximum component of the vector {tilde over (p)}({tilde over (k)}+1).The scaled vector {tilde over (p)}({tilde over (k)}+1) is used fortransmitting signals during the iteration cycle {tilde over (k)}+1 overthe transmission lines L₁ to L_(M). Scaling causes the input power level{tilde over ({circumflex over (p)}({tilde over (k)}+1)_(M) of thelongest transmission line L_(M) to be constant.

According to a further embodiment, the vector {tilde over (p)}({tildeover (k)}+1) of equation (24) is shifted once more:{tilde over ({tilde over (p)}({tilde over (k)}+1)=|{tilde over(p)}({tilde over (k)}+1)−{tilde over ({tilde over (g)}·{tilde over(d)}({tilde over (k)})·p _(max)|  (28)In equation (28) {tilde over ({tilde over (g)} is a predeterminedconstant. The vector {tilde over ({tilde over (p)}({tilde over (k)}+1)may be scaled:

$\begin{matrix}{{\hat{\overset{\sim}{\overset{\sim}{p}}}\left( {\overset{\sim}{k} + 1} \right)} = {{\overset{\sim}{\overset{\sim}{p}}\left( {\overset{\sim}{k} + 1} \right)} \cdot \frac{p_{\max}}{\max\left( {\overset{\sim}{\overset{\sim}{p}}\left( {\overset{\sim}{k} + 1} \right)} \right)}}} & (29)\end{matrix}$

The termination condition of the iterative method is:min(Sndb({tilde over (k)} _(max))_(i))<min(Sndb(k _(max)))−Δdb  (30)According to equation (30) the iterative method is terminated or atleast interrupted if at least one of the measured logarithmicsignal-to-noise ratios at a iteration cycle {tilde over (k)}_(max) fallsbelow the difference min(Sndb(k_(max)))−Δdb. In this case the iterativemethod is either terminated or it is started again with smallerconstants {tilde over (g)} and {tilde over ({tilde over (g)}. Forrestarting the iterative method input power levels {tilde over(p)}({tilde over (k)}<{tilde over (k)}_(max)) are used.

In the following a simulation is presented which illustrates theiterative method described above. The simulated network is a VDSLnetwork and comprises 25 transmission lines L₁ to L₂₅ in a cable C. Thelengths of the transmission lines L₁ to L₂₅ are evenly distributedbetween 200 m and 700 m. The network is based on a model as shown inFIG. 3. The type of interference is self-FEXT and alien noise. Theparameter Δdb is set to 3 dB. For the function {tilde over (F)} (cf.equation (26)) a linear function, a exponential function and alogarithmic function are chosen:

$\begin{matrix}{{\overset{\sim}{F}\left( \frac{{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{i}}{p_{\max}} \right)} = \frac{{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{i}}{p_{\max}}} & (31) \\{{\overset{\sim}{F}\left( \frac{{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{i}}{p_{\max}} \right)} = 100^{\frac{{\overset{\sim}{p}{(\overset{\sim}{k})}}_{i}}{p_{\max}}}} & (32) \\{{\overset{\sim}{F}\left( \frac{{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{i}}{p_{\max}} \right)} = {\log_{10}\left( \frac{{\overset{\sim}{p}\left( \overset{\sim}{k} \right)}_{i}}{p_{\max}} \right)}} & (33)\end{matrix}$

FIG. 9 shows a plot of the input power level p versus the length l ofthe transmission lines L₁ to L₂₅ and a plot of the resulting logarithmicsignal-to-noise ratio Sndb versus the length l in the presence of FEXTand alien noise. The three functions {tilde over (F)} according toequations (31) to (33) were used for the simulation. It is evident fromFIG. 9 that performing the iterative method described above results inbetter logarithmic signal-to-noise ratios for shorter transmissionlines, whereas the signal-to-noise ratios of the longer transmissionlines are only slightly decreased.

So far, methods for determining input power levels for a singlefrequency channel were discussed. In order to adjust the total powerspectrum density of all modems, the described iterative methods may beperformed for all frequency channels. For that, signals of differentfrequency channels can be transmitted over the transmission linessimultaneously.

In the following another example is presented in order to demonstratethe performance of the iterative methods discussed above. The example isbased on a VDSL network having a frequency band allocation as shown inFIG. 10. The maximum input power level is the same for all frequencychannels. The maximum power spectrum density is −59 dBm/Hz. In thisexample only the upstream direction is considered. The assumed powerspectral density of the alien noise is shown in FIG. 11. Allinterference signals caused by alien noise have the same power level.The alien noise is superposed by an additional white noise signal havinga power spectral density of −140 dBm/Hz. The simulated network comprises25 transmission lines L₁ to L₂₅ in a cable C. The lengths of thetransmission lines L₁ to L₂₅ are evenly distributed between 200 m and600 m. FIG. 12 shows the line attenuation of the shortest and thelongest transmission line. FIG. 13 shows the minimum and maximum FEXTattenuation. The factor K_(ij) is constant.

The predetermined parameter Δdb is modified in order to be dependent onthe fraction of the alien noise. The modified parameter Δ db(f) iscalculated for each frequency channel as follows:

$\begin{matrix}{{\Delta\;{\overset{\_}{db}(f)}} = {{\left( \frac{\eta(f)}{\eta_{\max}} \right)^{4} \cdot \Delta}\;{{db}.}}} & (34)\end{matrix}$

FIGS. 14 and 15 illustrate the results of the simulation. The inputpower levels p for each of the transmission lines L₁ to L₂₅ are shown.The maximum bit rates for each of the transmission lines L₁ to L₂₅ arealso shown. The maximum bit rates were calculated by adding the maximumbit rates of each frequency channel, which were derived from thelogarithmic signal-to-noise ratios. The parameter Δdb was set to 3 dBfor the simulation illustrated in FIG. 14 and 6 dB for the simulationillustrated in FIG. 15. FIG. 16 shows the spectral power density of theshortest and the longest transmission line for Δdb=3 dB and Δdb=6 dB.

FIG. 17 illustrates the results of another simulation. Here, thetransmission lines L₁ to L₂₅ have lengths between 200 m and 600 m, whichare statistically distributed. The factor K_(ij) and the alien noise arealso statistically distributed to a certain degree. The parameter Δdbwas set to 6 dB.

In addition, while a particular feature or aspect of an embodiment mayhave been disclosed with respect to only one of several implementations,such feature or aspect may be combined with one or more other featuresor aspects of the other implementations as may be desired andadvantageous for any given or particular application. Furthermore, tothe extent that the terms “include”, “have”, “with”, or other variantsthereof are used in either the detailed description or the claims, suchterms are intended to be inclusive in a manner similar to the term“comprise”. The terms “coupled” and “connected”, along with derivativesmay have been used. It should be understood that these terms may havebeen used to indicate that two elements co-operate or interact with eachother regardless whether they are in direct physical or electricalcontact, or they are not in direct contact with each other. Furthermore,it should be understood that embodiments may be implemented in discretecircuits, partially integrated circuits or fully integrated circuits orprogramming means. Also, the term “exemplary” is merely meant as anexample, rather than the best or optimal. It is also to be appreciatedthat features and/or elements depicted herein are illustrated withparticular dimensions relative to one another for purposes of simplicityand ease of understanding, and that actual dimensions may differsubstantially from that illustrated herein.

1. A method, wherein the following steps are iteratively repeated,comprising: providing each of a plurality of signals at a respective oneof a plurality of transmission links, the transmission links being wiredlines wherein neighboring ones of the transmission links are distortedby cross-talk interference; transmitting each of the plurality ofsignals over the respective one of the plurality of transmission links;and measuring signal-to-noise ratios of the plurality of signalstransmitted over the plurality of transmission links, wherein an inputpower level of each of the plurality of signals is set such that thesignal-to-noise ratios of the plurality of signals converge whenmeasured after their transmission over the plurality of transmissionlinks; wherein, at each iteration cycle, the input power level of eachof the plurality of signals when provided at the respective one of theplurality of transmission links depends on the difference of themeasured signal-to-noise ratio of the signal transmitted over therespective one of the plurality of transmission links during theprevious iteration cycle and an average value of the measuredsignal-to-noise ratios of the plurality of signals transmitted over theplurality of transmission links during the previous iteration cycle. 2.The method of claim 1, wherein the input power level of each of theplurality of signals is predetermined at the first iteration cycle. 3.The method of claim 1, wherein the input power level of each of theplurality of signals is set to the highest input power level at thefirst iteration cycle.
 4. The method of claim 1, wherein the input powerlevel of each of the plurality of signals when provided to therespective one of the plurality of transmission links during the seconditeration cycle depends on the inverted value of the measuredsignal-to-noise ratio of the signal transmitted over the respective oneof the plurality of transmission links during the first iteration cycle.5. The method of claim 1, wherein each of the plurality of transmissionlinks is a transmission line.
 6. The method of claim 1, wherein xDSL isused as service for transmitting data over the transmission links. 7.The method of claim 1, wherein each of the plurality of signals istransmitted in upstream direction over the respective one of theplurality of transmission links.
 8. The method of claim 1, wherein theinput power levels, at which the signal-to-noise ratios converge, areused for transmitting further signals.
 9. The method of claim 1, whereinthe method is performed when initializing the plurality of transmissionlinks.
 10. The method of claim 1, wherein the transmission links aretwisted wire pairs.
 11. The method of claim 1, wherein the plurality ofsignals are transmitted by electrical transmission.
 12. The method ofclaim 1, wherein at least two of the wired lines have different lengths.13. A method, wherein the following steps are iteratively repeated,comprising: providing each of a plurality of signals at a respective oneof a plurality of transmission links, the transmission links being wiredlines wherein neighboring ones of the transmission links are distortedby cross-talk interference; transmitting each of the plurality ofsignals over the respective one of the plurality of transmission links;and measuring signal-to-noise ratios of the plurality of signalstransmitted over the plurality of transmission links, wherein an inputpower level of each of the plurality of signals is set such that thesignal-to-noise ratios of the plurality of signals converge whenmeasured after their transmission over the plurality of transmissionlinks; wherein the input power level of each of the plurality of signalswhen provided at the respective one of the plurality of transmissionlinks depends on a product having at least a first factor and a secondfactor; the first factor depends on the input power level of the signalprovided at the respective one of the plurality of transmission linksduring the previous iteration cycle; and the second factor depends onthe difference of the measured signal-to-noise ratio of the signaltransmitted over the respective one of the plurality of transmissionlinks during the previous iteration cycle and an average value of themeasured signal-to-noise ratios of the plurality of signals transmittedover the plurality of transmission links during the previous iterationcycle.
 14. A method, wherein the following steps are iterativelyrepeated, comprising: for a plurality of transmission lines being wiredlines wherein neighboring ones of the transmission lines are distortedby cross-talk interference, each of the transmission lines having aninput terminal and an output terminal, providing each of a plurality offirst signals at the input terminal of a respective one of the pluralityof transmission lines and receiving each of the plurality of transmittedfirst signals at the output terminal of the respective one of theplurality of transmission lines; measuring signal-to-noise ratios of theplurality of transmitted first signals received at the output terminals;and providing each of a plurality of second signals at the inputterminal of a respective one of the plurality of transmission lines,wherein an input power level of each of the plurality of second signalswhen provided to the input terminal of the respective one of theplurality of transmission lines is set depending on the measuredsignal-to-noise ratios of the plurality of transmitted first signals;wherein, at each iteration cycle, the input power level of each of theplurality of signals when provided at the respective one of theplurality of transmission links depends on the difference of themeasured signal-to-noise ratio of the signal transmitted over therespective one of the plurality of transmission links during theprevious iteration cycle and an average value of the measuredsignal-to-noise ratios of the plurality of signals transmitted over theplurality of transmission links during the previous iteration cycle. 15.The method of claim 14, wherein each of the plurality of first signalswhen provided to the input terminal of the respective one of theplurality of transmission lines has a predetermined input power level.16. The method of claim 14, wherein each of the plurality of firstsignals when provided to the input terminal of the respective one of theplurality of transmission lines has the highest input power level.
 17. Amethod, wherein the following steps are iteratively repeated,comprising: for a plurality of transmission lines being wired lineswherein neighboring ones of the transmission lines are distorted bycross-talk interference, each of the transmission lines having an inputterminal and an output terminal, providing each of a plurality of firstsignals at the input terminal of a respective one of the plurality oftransmission lines and receiving each of the plurality of transmittedfirst signals at the output terminal of the respective one of theplurality of transmission lines; measuring signal-to-noise ratios of theplurality of transmitted first signals received at the output terminals;providing each of a plurality of second signals at the input terminal ofa respective one of the plurality of transmission lines, wherein aninput power level of each of the plurality of second signals whenprovided to the input terminal of the respective one of the plurality oftransmission lines is set depending on the measured signal-to-noiseratios of the plurality of transmitted first signals; wherein themeasured signal-to-noise ratios of the plurality of transmitted firstsignals are distributed over a first range of signal-to-noise ratios;and the input power level of each of the plurality of second signalswhen provided to the input terminal of the respective one of theplurality of transmission lines is set in such a manner that thesignal-to-noise ratios of the plurality of second signals after beingreceived at the output terminals are distributed over a second range ofsignal-to-noise ratios which is smaller than the first range ofsignal-to-noise ratios.
 18. A method, wherein the following steps areiteratively repeated, comprising: for a plurality of transmission linesbeing wired lines wherein neighboring ones of the transmission lines aredistorted by cross-talk interference, each of the transmission lineshaving an input terminal and an output terminal, providing each of aplurality of first signals at the input terminal of a respective one ofthe plurality of transmission lines and receiving each of the pluralityof transmitted first signals at the output terminal of the respectiveone of the plurality of transmission lines; measuring signal-to-noiseratios of the plurality of transmitted first signals received at theoutput terminals; and providing each of a plurality of second signals atthe input terminal of a respective one of the plurality of transmissionlines, wherein an input power level of each of the plurality of secondsignals when provided to the input terminal of the respective one of theplurality of transmission lines is set depending on the measuredsignal-to-noise ratios of the plurality of transmitted first signals;wherein the input power level of each of the plurality of second signalswhen provided to the input terminal of the respective one of theplurality of transmission lines depends on a product having at least afirst factor and a second factor; the first factor depends on the inputpower level of the first signal when provided to the input terminal ofthe respective one of the plurality of transmission lines; and thesecond factor depends on the difference of the measured signal-to-noiseratio of the first signal transmitted over the respective one of theplurality of transmission lines and an average value of the measuredsignal-to-noise ratios of the plurality of transmitted first signals.19. A method, wherein the following steps are iteratively repeated,comprising: providing an input power level for each of a plurality oftransmission links, the transmission links being wired lines whereinneighboring ones of the transmission lines are distorted by cross-talkinterference wherein the input power levels are provided in such amanner that when providing each of a plurality of first signals to arespective one of a plurality of transmission links having the providedinput power level and transmitting each of the plurality of firstsignals over the respective one of the plurality of transmission links,the signal-to-noise ratios of the plurality of transmitted first signalsare equal; and iteratively repeating the following steps: providing eachof a plurality of second signals to a respective one of a plurality oftransmission links; transmitting each of the plurality of second signalsover the respective one of the plurality of transmission links; andmeasuring signal-to-noise ratios of the plurality of second signalstransmitted over the plurality of transmission links, wherein at eachiteration cycle an input power level of at least one of the plurality ofsecond signals when provided to the respective one of the plurality oftransmission links is increased; wherein, at each iteration cycle, theinput power level of each of the plurality of second signals whenprovided at the respective one of the plurality of transmission linksdepends on the difference of the measured signal-to-noise ratio of thesignal transmitted over the respective one of the plurality oftransmission links during the previous iteration cycle and an averagevalue of the measured signal-to-noise ratios of the plurality of signalstransmitted over the plurality of transmission links during the previousiteration cycle.
 20. The method of claim 19, wherein, at the firstiteration cycle, the input power level of the at least one of theplurality of second signals when provided to the respective one of theplurality of transmission links is greater than the provided input powerlevel for the respective one of the plurality of transmission links. 21.The method of claim 19, wherein the method is terminated when themeasured signal-to-noise ratio of at least one of the plurality oftransmitted second signals exceeds a predetermined threshold.
 22. Amethod, wherein the following steps are iteratively repeated,comprising: providing an input power level for each of a plurality oftransmission links, the transmission links being wired lines whereinneighboring ones of the transmission lines are distorted by cross-talkinterference wherein the input power levels are provided in such amanner that when providing each of a plurality of first signals to arespective one of a plurality of transmission links having the providedinput power level and transmitting each of the plurality of firstsignals over the respective one of the plurality of transmission links,the signal-to-noise ratios of the plurality of transmitted first signalsare equal; and iteratively repeating the following steps: providing eachof a plurality of second signals to a respective one of a plurality oftransmission links; transmitting each of the plurality of second signalsover the respective one of the plurality of transmission links; andmeasuring signal-to-noise ratios of the plurality of second signalstransmitted over the plurality of transmission links, wherein at eachiteration cycle an input power level of at least one of the plurality ofsecond signals when provided to the respective one of the plurality oftransmission links is increased; wherein the input power level of the atleast one of the plurality of second signals when provided to therespective one of the plurality of transmission links depends on aproduct having at least a first factor and a second factor; the firstfactor depends on the input power level of the second signal whenprovided to the respective one of the plurality of transmission linksduring the previous iteration cycle; and the second factor depends on alinear function or an exponential function or a logarithmic function ofthe input power level of the second signal transmitted over therespective one of the plurality of transmission links during theprevious iteration cycle.
 23. A non-transitory computer readable mediumcomprising: computer executable code for executing a method according toclaim 1 on a computer system.
 24. A device, comprising: a plurality ofoutput terminals to provide a plurality of signals to a plurality oftransmission links, the transmission links being wired lines whereinneighboring ones of the transmission lines are distorted by cross-talkinterference; a plurality of input terminals to receive signal-to-noiseratios of the plurality of signals transmitted over the plurality oftransmission links; and a plurality of setting circuits to set inputpower levels of the plurality of signals provided to the plurality oftransmission lines, wherein the input power level of each of theplurality of signals is set such that the signal-to-noise ratios of theplurality of signals converge when measured after their transmissionover the plurality of transmission links; wherein, the input power levelof each of the plurality of signals when provided at the respective oneof the plurality of transmission links depends on the difference of themeasured signal-to-noise ratio of the signal transmitted over therespective one of the plurality of transmission links during theprevious iteration cycle and an average value of the measuredsignal-to-noise ratios of the plurality of signals transmitted over theplurality of transmission links during the previous iteration cycle. 25.The device of claim 24, wherein the input power levels, at which thesignal-to-noise ratios converge, are used for transmitting furthersignals.
 26. A system, comprising: a plurality of transmission linksbeing wired lines wherein neighboring ones of the transmission lines aredistorted by cross-talk interference; a plurality of transmitters toprovide a plurality of signals to the plurality of transmission links; aplurality of receivers to receive the plurality of signals transmittedover the plurality of transmission links; a plurality of measuringcircuits to measure signal-to-noise ratios of the plurality of signalstransmitted over the plurality of transmission links; and a plurality ofsetting circuits to set input power levels of the plurality of signalsprovided to the plurality of transmission lines, wherein the input powerlevel of each of the plurality of signals is set such that thesignal-to-noise ratios of the plurality of signals converge whenmeasured after their transmission over the plurality of transmissionlinks; wherein, the input power level of each of the plurality ofsignals when provided at the respective one of the plurality oftransmission links depends on the difference of the measuredsignal-to-noise ratio of the signal transmitted over the respective oneof the plurality of transmission links during the previous iterationcycle and an average value of the measured signal-to-noise ratios of theplurality of signals transmitted over the plurality of transmissionlinks during the previous iteration cycle.
 27. The system of claim 26,wherein the input power level of each of the plurality of signalsdepends on the measured signal-to-noise ratios of the plurality ofsignals transmitted over the plurality of transmission links during aprevious transmission cycle.
 28. The system of claim 26, wherein theinput power levels, at which the signal-to-noise ratios converge, areused for transmitting further signals.